The nominee to replace Kathleen Sebelius, budget director Sylvia Mathews Burwell, is likely to be confirmed by Senate Democrats.

WASHINGTON — President Obama named White House budget director Sylvia Mathews Burwell to take over the Department of Health and Human Services on Friday, saying there was "no manager as experienced and as competent" to oversee the next phase of his signature healthcare law.

"Sylvia was a rock, a steady hand on the wheel" as the administration dealt with the government shutdown last year, Obama told a crowd gathered in the White House Rose Garden. Burwell, he said, helped reach a two-year budget deal that "put an end to these manufactured crises that we had seen here in Washington."

Burwell's nomination follows the resignation of Kathleen Sebelius, who ran the agency for a five-year period that included the troubled launch of the federal online insurance marketplace, a fiasco that threatened the viability of the Affordable Care Act, cost millions of dollars, depressed Obama's popularity and put Democratic control of the Senate at risk.

With Burwell, who was unanimously confirmed by the Senate to her current post, the White House hopes to ensure the continued rollout of the healthcare law offers Republicans no more ammunition to attack it. Obamacare has shaped up to be one of the major issues in the midterm elections.

Burwell's confirmation hearings, however, are likely to be boisterous, as Republicans dissect what they see as the healthcare law's failures and grill a nominee in line for a job the GOP calls the "chief implementer of Obamacare."

But Burwell has already won some GOP support. Sen. John McCain (R-Ariz.) said she was "an excellent choice" and Rep. Paul D. Ryan (R-Wis.) called her "a consummate professional." Even without Republican support, Burwell is likely to be confirmed by Senate Democrats under new filibuster rules that require just a simple majority vote.

Although the HealthCare.gov website has been fixed and 7.5 million people have now enrolled, it remains unclear how well the program will work in its critical first year. Any stumbles could rejuvenate GOP opposition to the health law.

In the next few months, health insurers will begin to price premiums for 2015 in preparation for the next enrollment period that opens in November. Several insurance industry officials have warned that they may seek double-digit increases in premiums for 2015 because they did not get enough healthy enrollees in the first year.

That has set off a scramble at HHS and the White House, which fears a series of major rate hikes.

The GOP senses an opportunity, given the law's continued unpopularity. A recent Gallup Poll found that 54% of Americans disapprove of the law, while 43% approve.

Burwell faces two confirmation hearings before the Senate finance and health committees. Both hearings, and the floor debate, promise an outlet for Republicans to renew their assault on Obamacare. Republicans have been seeking to force Democrats to cast votes on the law, but Majority Leader Harry Reid (D-Nev.) has largely prevented that.

Senate Democrats in difficult reelection campaigns may also use the process to demonstrate independence from the White House.

Democratic Sen. Joe Manchin III praised Burwell, who was born in his home state of West Virginia and whose mother was mayor of Hinton, W.Va., when he was the state's governor. But he said her nomination offers a chance for a fresh start for Democrats like him who have sought to improve the law.

"It gives us a chance to really repair — in a bipartisan manner, hopefully — all of the things that moderate and conservative Democrats think need to be repaired," he said.

Manchin has called for delaying for a year the law's requirement that individuals have health insurance or pay a fine. And he is one of six senators — five Democrats and an independent — who last month introduced bills to make changes to the law. Reid has not brought those proposals to the floor, but those senators could press Burwell to consider them.

"I think Sylvia will seriously look at these changes and see if they have merit," Manchin said.

In appointing Burwell, advisors to the president say he is putting his best manager into the position. A veteran of the Clinton administration, Burwell served as head of two major philanthropic organizations before joining the Obama administration. She graduated with honors from Harvard University and holds a bachelor's degree in philosophy, politics and economics from Oxford University, where she was a Rhodes Scholar.

Appearing with the president Friday, Burwell made just a few brief comments, saying she was "excited by the opportunity" to "carry on the important work" at Health and Human Services.

Also in the Rose Garden was Sebelius, whom the president praised for her devotion to healthcare reform. Under her leadership, Obama said, the federal website was fixed.

"The final score speaks for itself," he said.

In her remarks, Sebelius called Obamacare "the most significant social change in this country" in 50 years.

"We are on the front lines of a long overdue national change — fixing a broken health system," she said. "This is the most meaningful work I've ever been a part of. In fact, it's been the cause of my life. And I knew it wouldn't be easy."